Tube with conductive fins

ABSTRACT

A tube includes a center tube comprising a steel material, a fluid flowing through the center tube; and at least one disk disposed around the center tube, the disk including a thermally conductive material and exposed to an external heat source. The disk conducts heat from the external heat source into the center tube. The center tube transfers the heat from the external heat source into the fluid. The thermal conductivity of the at least one disk is higher than the thermal conductivity of the center tube.

BACKGROUND

The present subject matter relates generally to boiler and/or steam generator tubes, and more specifically to tubes with thermally conductive fins.

Heat recovery steam generators (HRSG), as well as boilers more generally, include several possible configurations including various arrangements of piping, tubes, orifices, baffles, flow conduits, and other components. Heat recovery steam generators installed at power plants use exhaust gases from gas turbine engines to produce steam at various pressures, temperatures, and flow rates for use in power-producing steam turbine generators, as well as for other processes and/or purposes (for example, at co-gen facilities).

Heat recovery steam generators may include high-pressure, intermediate-pressure, and low-pressure systems (referring to the pressure of the steam) which may include drums. Heat recovery steam generators (HRSG) may include tubes, the exterior portions of which are exposed to hot exhaust gas from the gas turbine, and the interior of which include fluids such as water and/or steam flowing therethrough. The effectiveness with which the tubes transfer heat from the exhaust gas to the fluid (i.e., water, steam, and/or other fluids such as ammonia) directly affects the effectiveness of the HRSG, and in turn the overall efficiency of the power plant and/or other facility in which the HRSG is installed.

HRSG and tube effectiveness depends on a number of factors including the surface area of the tubes, the internal flow area of the tubes, and the heat conductivity of the tube material. In addition, other design constraints factor into the design of HRSG including ensuring a minimal tube strength, accounting for pressure losses of the fluid within the tubes, initial construction costs, ongoing maintenance costs, as well as the general durability of the tubes, and their susceptibility to degradation.

BRIEF DESCRIPTION OF THE EMBODIMENTS

Aspects of the present embodiments are summarized below. These embodiments are not intended to limit the scope of the present claimed embodiments, but rather, these embodiments are intended only to provide a brief summary of possible forms of the embodiments. Furthermore, the embodiments may encompass a variety of forms that may be similar to or different from the embodiments set forth below, commensurate with the scope of the claims.

In one aspect, a tube includes a center tube comprising a steel material, a fluid flowing through the center tube; and at least one disk disposed around the center tube, the disk including a thermally conductive material and exposed to an external heat source. The disk conducts heat from the external heat source into the center tube. The center tube transfers the heat from the external heat source into the fluid. The thermal conductivity of the at least one disk is higher than the thermal conductivity of the center tube.

In another aspect, a method of forming a finned tube includes: disposing a conductive sheet material adjacent to a steel tube; winding the conductive sheet material around the steel tube; and welding the conductive sheet material to the steel tube using a high frequency welding process. The frequency of the high frequency welding process is between about 450 kHz and 1200 kHz.

In another aspect, an HRSG includes a tube with conductive fins according to the embodiments disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a side schematic representation of a heat recovery steam generator (HRSG);

FIG. 2 is a perspective view of a tube with thermally conductive fins;

FIG. 3 is an enlarged perspective view of a portion of a tube with thermally conductive fins;

FIG. 4 is a method of forming finned tubes;

FIG. 5 is a perspective view of a tube with thermally conductive fins; and

FIG. 6 is a perspective view of a tube with thermally conductive fins, according to aspects of the present embodiments.

Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of the disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of the disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein.

DETAILED DESCRIPTION

In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings.

The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

As used herein, the term “axial” refers to a direction aligned with a central axis or shaft of a generator and/or turbine, and/or aligned with the central axis of an HRSG tube. As used herein, the term “longitudinal” may be used synonymously with the term “axial.”

As used herein, the term “circumferential” refers to a direction or directions around (and tangential to) the outer circumference of the generator, turbine, and/or HRSG tube, or for example the circle defined by the swept area of the rotor of the generator and/or turbine. As used herein, the terms “circumferential” and “tangential” may be synonymous.

As used herein, the term “radial” refers to a direction moving outwardly away from the central axis of the generator, turbine and/or HRSG tube. A “radially inward” direction is aligned toward the central axis moving toward decreasing radii. A “radially outward” direction is aligned away from the central axis moving toward increasing radii.

FIG. 1 illustrates an exemplary heat recovery steam generator (HRSG) 10. The HRSG 10 may include a gas turbine exhaust portion 12 for receiving exhaust gases from a gas turbine (not shown). The HRSG 10 may also include a superheater section 16, an evaporator section 18, and an economizer section 20. Each of the superheater, evaporator, and economizer sections 16, 18, 20 may include a plurality of tubes 22, as well as other piping, baffles, and other components used to generate steam from the exhaust gases. The HRSG 10 may also include a stack 14 through which exhaust gases may exit after flowing through the HRSG 10. The HRSG 10 of FIG. 1 may be a conventional HRSG and/or a once-through HRSG, and as such, HRSG 10 may or may not include a high-pressure drum 24 and/or other drums (i.e., intermediate and/or low-pressure drums).

Referring still to FIG. 1, the HRSG 10 may include a feedwater source 26 for providing feedwater to the economizer section 20, as well as first and second steam lines 28, 30 for delivering steam to one or more steam turbines (not shown) and/or other downstream industrial processes. The superheater section 16 may include a first stage 32, as well as a second stage 34 fluidly coupled to the first stage 32 via one or more first interconnect lines 36. The first stage 32 may include a first steam header 38 while the second stage 34 may include a second steam header 40. The HRSG 10 may also include a duct burner 42 including a plurality of burners 44 for raising the temperature of the exhaust gases upstream of the superheater section 16. The HRSG 10 may also include a second interconnect line 46 fluidly coupling the superheater section 16 to the evaporator section 18 via the drum 24. The HRSG 10 may also include a third interconnect line 48 fluidly coupling the economizer section 20 to the evaporator section 18 via the drum 24. Each tube 22 within each of the superheater, evaporator, and economizer sections 16, 18, 20 may include an angled portion 60 to facilitate delivering the internal fluids (steam, water, ammonia, and/or other fluids) to one or more drums 24, headers 38, 40, and/or other conduits or plenums, while also maximizing the portion of each tube aligned in a vertical direction (i.e., normal to the direction in which oncoming exhaust gases are flowing, thereby enhancing heat transfer).

FIG. 2 illustrates a finned tube 22 according to the embodiments disclosed herein. The finned tube 22 includes a plurality of disks 50 disposed around a center tube 52 aligned in a longitudinal direction 72. Each disk may include a plurality of fin segments 58 extending radially outward from a disk center portion 74. The disk center portion 74 extends circumferentially around the outer circumference of the center tube 52. Each of the fin segments 58 is separated from an adjacent fin segment 58 by a serration 76. The center tube 52 may include a centerline 54 extending in a longitudinal direction 72 and defining the geometric center of the center tube 52, which may be substantially cylindrical. The center tube 52 may also include a hollow interior 56 through which fluids such as steam, water and/or, ammonia (as well as other fluids) may flow. Each disk 50 may be substantially planar and may be stacked such that it is disposed longitudinally above and/or below at least one adjacent disk 50. In one embodiment, each fin segment 58 of each disk 50 is circumferentially and/or longitudinally aligned with at least one fin segment 58 of an adjacent disk 50. In other embodiments, each fin segment 58 of each disk 50 is circumferentially and/or longitudinally offset from at least one fin segment 58 of an adjacent disk 50. In other embodiments, each fin segment 58 of each disk 50 may be either circumferentially and/or longitudinally offset from or aligned with at least one fin segment 58 of an adjacent disk 50. In other embodiments, the fin segments 58 may be arranged in a spiral configuration, an alternating pattern, and/or a random configuration relative to the fin segments 58 longitudinally above and/or below them.

Referring still to FIG. 2, the disk 50 may be at least partially composed of aluminum and/or other thermally conductive materials such as beryllium, copper, gold, magnesium, iridium, molybdenum, rhodium, silver, tungsten, and/or other suitable materials, as well as alloys thereof. The center tube 52 may be at least partially composed of carbon steel, alloy steel, stainless steel, ferritic stainless, austenitic stainless, and/or other materials that are sufficiently thermally conductive, stress tolerant, and temperature resistant. In some embodiments, the HRSG may include center tubes 52 in the superheater and/or evaporate sections 16, 18 that are composed of materials that are resistance to higher temperatures (for example 1100° F.). The HRSG may also include center tubes 52 in the economizer and/or evaporate sections 20, 18 that are composed of materials that have lower temperature resistance and higher thermal conductivity.

FIG. 3 illustrates a portion of the finned tube 22 including the center tube 52 disposed about the centerline 54, and the plurality of disks 50 disposed around the center tube 52. FIG. 3 also illustrates a tube outer radius 68, an inner circle outer radius 78, and a disk outer radius 70. The tube outer radius 68 may be defined as the distance from the exterior surface of the center tube 52 to the centerline 54. The inner circle outer radius 78 may be defined as the distance from a radially outer portion of the inner circle 74 to the centerline 54. The disk outer radius 70 may be defined as the distance from a radially outer portion of the disk 50 to the centerline 54. A fin height 80 may be defined as the difference between the disk outer radius 70 and the tube outer radius 78. In one embodiment, the disk outer radius 70 may be from about 1.25 to about 5.0 times the tube outer radius 68. In another embodiment, the disk outer radius 70 may be from about 1.5 to about 4.0 times the tube outer radius 68. In another embodiment, the disk outer radius 70 may be from about 2.0 to about 3.0 times the tube outer radius 68. In another embodiment, the disk outer radius 70 may be from about 2.25 to about 2.75 times the tube outer radius 68. In another embodiment, the disk outer radius 70 may be about 2.5 times the tube outer radius 68. In another embodiment, the disk outer radius 70 may be from about 1.1 to about 3.5 times the inner circle outer radius 78. In another embodiment, the disk outer radius 70 may be from about 1.25 to about 3.0 times the inner circle outer radius 78. In another embodiment, the disk outer radius 70 may be from about 1.5 to about 2.5 times the inner circle outer radius 78. In another embodiment, the disk outer radius 70 may be about 1.75 times the inner circle outer radius 78.

Referring still to FIG. 3, each disk 50 of the finned tube 22 may include a serration angle 66 defining the angular offset between each fin segment 58 and an adjacent fin segment 58. The serration angle 66 may be from about 4 degrees to about 30 degrees. In other embodiments, the serration angle 66 may be from about 7 degrees to about 25 degrees. In other embodiments, the serration angle 66 may be from about 10 degrees to about 20 degrees. In other embodiments, the serration angle 66 may be from about 12 degrees to about 18 degrees. In other embodiments, the serration angle 66 may be about 15 degrees. Each disk 50 may include from about 12 to about 100 fin segments 58. In other embodiments, each disk 50 may include from about 15 to about 80 fin segments 58. In other embodiments, each disk 50 may include from about 18 to about 60 fin segments 58. In other embodiments, each disk 50 may include from about 20 to about 40 fin segments 58. In other embodiments, each disk 50 may include from about 22 to about 30 fin segments 58. In other embodiments, each disk 50 may include about 24 fin segments 58. In some embodiments, each disk 50 disposed on a given finned tube 22 may include the same number of fin segments 58. In other embodiments, each disk 50 may include a different number of fin segments 58 than other disks 50 disposed on the same finned tube 22.

Still referring to FIG. 3, each fin segment 58 may include a fin segment width 82 defined at a radially outer portion of the fin. Each fin segment 58 may also be separated from an adjacent fin segment 58 by a fin segment spacing 64 (i.e., approximately equal to the width of the serration 76 defined at the widest (i.e., radially outer) portion of each serration 76). In some embodiments, the fin segment width 82 is about 0.5 to about 1.5 times the fin segment spacing 64. In other embodiments, the fin segment width 82 is about 0.75 to about 1.25 times the fin segment spacing 64. In other embodiments, the fin segment width 82 is about 0.85 to about 1.15 times the fin segment spacing 64. In other embodiments, the fin segment width 82 is approximately equal to the fin segment spacing 64. The finned tube 22 may include a disk spacing 62 defining a longitudinal gap between each disk 50 and an adjacent disk 50. The ratio of the disk spacing 62 to a fin thickness may be from about 1 to about 10. In other embodiments, the ratio of the disk spacing 62 to the fin thickness may be from about 1.5 to about 9. In other embodiments, the ratio of the disk spacing 62 to the fin thickness may be from about 2 to about 8. In other embodiments, the ratio of the disk spacing 62 to the fin thickness may be from about 3 to about 7. In other embodiments, the ratio of the disk spacing 62 to the fin thickness may be from about 4 to about 6. In other embodiments, the ratio of the disk spacing 62 to the fin thickness may be about 5.

Referring to still to FIG. 3, in some embodiments, the fin thickness may be from about 0.5 mm to about 1.5 mm. In other embodiments, the fin thickness may be from about 0.8 mm to about 1.2 mm. In other embodiments, the fin thickness may be about 1.0 mm. The fin height 80 may be from about 4 mm to about 25 mm. In other embodiments, the fin height 80 may be from about 6 mm to about 19 mm. In other embodiments, the fin height 80 may be from about 8 mm to about 16 mm. In other embodiments, the fin height 80 may be from about 10 mm to about 14 mm. The outer diameter of the center tube 52 may be from about 1.0 inch to about 2.5 inches. In other embodiments, the outer diameter of the center tube 52 may be from about 1.25 inch to about 2.0 inches. In other embodiments, the outer diameter of the center tube 52 may be less than 1.0 inch or more than 2.5 inches. The finned tube 22 may include from about 80 to about 450 disks 50 per meter of tube 52 (i.e., in the longitudinal direction 72). In other embodiments, the finned tube 22 may include from about 100 to about 400 disks 50 per meter of tube 52. In other embodiments, the finned tube 22 may include from about 120 to about 330 disks 50 per meter of tube 52. In other embodiments, the finned tube 22 may include from about 150 to about 300 disks 50 per meter of tube 52. In some embodiments, the ends of the center tube 52 may be un-finned to allow for connection of the center tube 52 to other components. For example, from about 50 mm to about 150 mm of the center tube 52 may be un-finned at either end and/or at both ends.

FIG. 4 illustrates a method 400 of forming the finned tube 22. At step 402, the method 400 includes placing serrations into conductive sheet material. The conductive sheet material may include sheet metal comprising aluminum, beryllium, copper, gold, magnesium, iridium, molybdenum, rhodium, silver, tungsten, and/or other materials and alloys thereof. A rotary serrator may be used to place the serrations into the conductive sheet material. The spacing between serrations may be approximately equal to a desired fin segment width 82. The length of each serration may be approximately equal to a desired fin segment height 84. At step 404, the method 400 includes placing the conductive sheet material adjacent a steel tube 52. The steel tube 52 may be at least partially composed of carbon steel, alloy steel, stainless steel, ferritic stainless, austenitic stainless, and/or other materials that are sufficiently thermally conductive, stress tolerant, and temperature resistant. At step 406, the method 400 includes welding the conductive sheet metal to the steel tube 52 via a high frequency welding process (for example using high frequency spiral fin welding). The frequency of the high frequency welding process may be from about 450 kHz to about 1200 kHz. In other embodiments, the frequency of the high frequency welding process may be from about 500 kHz to about 1100 kHz. In other embodiments, the frequency of the high frequency welding process may be from about 600 kHz to about 1000 kHz. In other embodiments, the frequency of the high frequency welding process may be from about 700 kHz to about 900 kHz. In other embodiments, the frequency of the high frequency welding process may be about 800 kHz.

Still referring the FIG. 4, at step 408, the method 400 may include winding the conductive sheet material (i.e., the aluminum strip) around the steel tube 52. As the aluminum strip comes into contact with the steel tube 52, the high frequency welding is performed at the interface between the conductive metal sheet (i.e., aluminum strip) and the steel tube 52, thereby permanently welding the aluminum strip to the steel tube 52. At step 410, the method 400 may include opening the serrations 76 as the aluminum strip is wrapped around the steel tube 52, thereby forming the fin segments 58. The opening of the serrations 76 may happen automatically as a natural result of the winding process. At step 412, the method may include bonding the ends of the aluminum strip together, once the aluminum strip has been wrapped all the way around the steel tube 52. The ends of the conductive sheet material (e.g., aluminum strip) may be bonded together via welding, brazing, high temperature epoxy, and/or other suitable bonding processes, thereby forming the disks 50. At step 414, the method 400 may include coating the steel tube 52 with rust inhibitor via a pump and/or spray nozzle. At step 416, the method 400 may include heat treating the steel tube 52 and disk 50. Steps 402 through 414 may be repeated prior to step 416, thereby disposing more disks 50 onto the steel tube 52 prior to performing the heat treat process at step 416. In other embodiments, the steps may be performed in other orders and/or concurrently. For example, steps 406, 408, and 410 may all be performed virtually simultaneously. In addition, other steps may be performed that are not shown in FIG. 4. In addition, in some embodiments, not all of the steps illustrated in FIG. 4 may be performed. Method 400 may also be used to join other highly conductive materials and components to other steel materials and components.

FIG. 5 illustrates an embodiment of the finned tube 22 (including fin segments, and a center tube 52 disposed about center line 54) in which each disk 50 is rotated from the disk above and/or below it with respect to a longitudinal direction 72. The embodiment of the finned tube 22 according to FIG. 5 may provide enhanced heat transfer due to an increased amount of surface area on the plurality of fin segments 58 that is in the path of and/or proximate to flow of exhaust gases in the HRSG 10.

FIG. 6 illustrates an embodiment of the finned tube 22 (including fin segments, and a center tube 52 disposed about center line 54) in which each disk 50 is connected to at least one disk 50 below or above it relative to a longitudinal direction 72. Stated otherwise, the finned tube 22 of FIG. 6 includes disks 50 that wrap around the center tube 50 in a spiral configuration from one end of the center tube to the other 50. As such, the finned tube 22 may include both a terminal fin segment 88 and a fin segment edge 86 disposed at each end of the finned tube 22. The disks 50 according to the spiral configuration of FIG. 6 may be disposed around center tube 52 via high frequency spiral fin welding according to method 400.

In operation, heat from the gas stream from the gas turbine exhaust is transferred through the thermally conductive fin segments 58, into the center tube 52, and eventually into the fluid flowing through the center tube 52. HRSGs employing the finned tube 22 of the present embodiment may utilize finned tubes 22 for the lowest temperature 30-40% of the tubes. Stated otherwise, the 40% of HRSG tubes that are closest to the stack may employ the finned tube 22 configuration of the present embodiments, while tubes closer to the gas turbine exhaust may include a conventional design. In other embodiments, the 30% of HRSG tubes that are closest to the stack may employ the finned tube 22 configuration of the present embodiments. In other embodiments, the 20% of HRSG tubes that are closest to the stack may employ the finned tube 22 configuration of the present embodiments. In other embodiments, the 10% of HRSG tubes that are closest to the stack may employ the finned tube 22 configuration of the present embodiments. By including disks 50 composed of thermally conductive material around the center tube 22, an increase in the effectiveness of heat transfer into thermal energy (for use in a power generation facility or other application) may be realized. The embodiments disclosed herein may include disks 50 that are substantially circular and/or ring-shaped rather than segmented or serrated (i.e., continuous, un-segmented disks). In addition, by using a mix of materials (such as aluminum, beryllium, copper, gold, magnesium, iridium, molybdenum, rhodium, silver, tungsten, and also carbon steel, stainless steel, ferritic stainless, and/or austenitic stainless) with a mix of material properties (including thermal conductivity, temperature resistance, and stress tolerance) HRSG tubes that are both robust and effective at transferring heat may be realized. As such, the disk 50 may be composed of a material with a higher thermal conductivity than that of the center tube 52.

The present embodiments have been described primarily in terms of applications within heat recovery steam generators (HRSG). However, several other applications are possible. Exemplary applications of the present embodiments may include tubes within steam turbine boilers, once-through HRSGs, steam production boilers, conventional boilers, HVAC systems, heat exchangers, radiators, automobiles, condensers, chillers, refrigeration equipment and/or other types of equipment where enhanced heat transfer is desired. The embodiments disclosed herein enable highly thermally conductive materials such as aluminum and/or copper to be welded to high strength and temperature resistance materials such as various types of steels via high frequency spiral fin welding, which in turn enables an increased heat transfer effectiveness and higher overall efficiency in heat recovery steam generator (HRSG) and/or power generator applications.

Although specific features of various embodiments of the present disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the present disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.

This written description uses examples to disclose the embodiments of the present disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the embodiments described herein is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 

What is claimed is:
 1. A tube comprising: a center tube comprising a steel material, a fluid flowing through the center tube; and at least one disk disposed around the center tube, the at least one disk comprising a thermally conductive material, the at least one disk exposed to an external heat source, wherein the at least one disk conducts heat from the external heat source into the center tube; wherein the center tube transfers the heat from the external heat source into the fluid, and wherein a thermal conductivity of the at least one disk is higher than a thermal conductivity of the center tube.
 2. The tube of claim 1, further comprising at least one fin segment disposed in the at least one disk.
 3. The tube of claim 1, wherein the at least one disk is bonded to the center tube via a high-frequency welding process.
 4. The tube of claim 1, wherein the at least one disk further comprises a continuous ring-shaped disk.
 5. The tube of claim 1, wherein the at least one disk is at least partially composed of at least one of aluminum, beryllium, copper, gold, magnesium, iridium, molybdenum, rhodium, silver, and tungsten.
 6. The tube of claim 1, wherein the center tube is at least partially composed of at least one of carbon steel, alloy steel, stainless steel, ferritic stainless, and austenitic stainless.
 7. The tube of claim 1, further comprising multiple disks, wherein the tube comprises between about 80 and about 450 disks per meter of tube length.
 8. The tube of claim 7, wherein at least one disk of the multiple disks is longitudinally aligned with at least one adjacent disk.
 9. The tube of claim 7, wherein the at least one disk wraps around the center tube in a spiral configuration.
 10. The tube of claim 1, wherein the at least one disk comprises a thickness between about 0.5 mm and about 1.5 mm.
 11. The tube of claim 2, wherein the at least one disk comprises a fin height of between about 4 mm and about 25 mm.
 12. The tube of claim 2, wherein the at least one disk comprises between about 12 fin segments and about 100 fin segments.
 13. The tube of claim 1, wherein a tube outer diameter is between about 1 inch and about 2.5 inches.
 14. A heat recovery steam generator (HRSG) comprising at least one tube according to claim
 1. 15. The HRSG of claim 14, wherein at least about 10% of the tubes of the HRSG comprise the tube according to claim
 1. 16. The HRSG of claim 15, further comprising: at least one fin segment disposed in the at least one disk; wherein the at least one disk wraps around the center tube in a spiral configuration, wherein the at least one disk is bonded to the center tube via a high-frequency welding process, wherein the at least one disk is at least partially composed of at least one of aluminum and copper, wherein the center tube is at least partially composed of at least one of carbon steel, alloy steel, stainless steel, ferritic stainless, and austenitic stainless, wherein the at least one disk comprises a thickness between about 0.5 mm and about 1.5 mm, wherein the at least one disk comprises a fin height between about 4 mm and about 25 mm, wherein the at least one disk comprises between about 12 fin segments and about 100 fin segments, and wherein a tube outer diameter is between about 1 inch and about 2.5 inches.
 17. A method of forming a finned tube comprising: disposing a conductive sheet material adjacent to a steel tube; winding the conductive sheet material around the steel tube; and welding the conductive sheet material to the steel tube using a high frequency welding process; wherein the frequency of the high frequency welding process is between about 450 kHz and 1200 kHz.
 18. The method of claim 17, further comprising serrating the conductive sheet material prior to disposing the conductive sheet material adjacent to the steel tube.
 19. The method of claim 17, wherein the conductive sheet material at least partially comprises at least one of aluminum and copper.
 20. The method of claim 18, further comprising: coating the steel tube with a rust inhibitor after welding the conductive sheet material to the steel tube using a high frequency welding process; and heat treating the steel tube and conductive sheet material. 